1. Field of the Invention
The present invention relates to a method for changing a boundary surface tension of a liquid glass piece. It also relates to an apparatus for performing that method.
2. Description of the Related Art
Currently after a casting process for making them manufactured optical lenses and also other curved glass bodies are ground in several grinding or working steps, which provide them with a predetermined radius of curvature. The individual grinding and polishing steps however cause high manufacturing costs because they are highly time consuming and because of the expensive machine engineering.
A generic process is disclosed in U.S. Pat. No. 3,535,100, in which the shape of a liquid glass piece is changed. In this process the liquid glass piece is supported on an electrically conducting support and an electrical potential is applied to the liquid glass piece by contacts connectable with the liquid glass piece.
The electrically conducting support itself is an electrically conducting liquid in the case of this reference. Current flow within the liquid glass piece changes the boundary surface tension, which changes the shape of the glass sample. Problems are encountered using this process for optical glass, which has high specifications in regard to shaping and purity. The reason for this is the inhomogeneous behavior of ions contained in the liquid glass piece, especially alkali ions, with progressing time, since the liquid glass piece cools over the course of time.